1. Field of the Invention
The present invention relates to an optical disc reproducing system such as a compact disc player (CDP), a digital versatile disc player (DVDP) or a digital versatile disc ROM (DVDROM), and more particularly, to a brake signal generating circuit for improving the efficiency of a lens brake in an optical disc reproducing system and a method thereof.
2. Description of the Related Art
Typically, an optical disc reproducing system includes a spindle motor for rotating an optical disc, a focus actuator for emitting a laser beam onto the optical disc, a tracking actuator for tracing a track of the optical disc, and a sled motor for operating a pickup.
To quickly find data recorded in the optical disc, the tracking actuator or the sled motor is used to jump tracks. Immediately after jumping the tracks, a tracking pull-in needs to be performed so that the found data can be reproduced normally. However, the inertia after the track jump may cause the tracking actuator to be pulled out which leads to the failure of the tracking pull-in. As a solution to this problem, a brake signal generating circuit is used.
A brake signal generating circuit used in existing optical disc reproducing systems will be described with reference to the attached drawings.
For example, in a compact disc using 3 beam signals, a main beam is located at the center of a track of the disc, an F beam (side beam) is located at the upper right side of the track of the disc and an E beam (side beam) is located at the lower left side of the track of the disc. When the main beam moves along a pit, a radio frequency output (RFO) signal is generated due to the current difference resulting from the reflection between the pit and a mirror. If the RFO signal moves the mirror between tracks for the track jump, the amount of the emitted beams increases and the lower part of the RFO signal looks like a sine wave. The RFO signal is shown in (b) of FIGS. 3A and 3B. A mirror signal MIRR detects the track movement of the main beam using the tilt of the RFO signal generated when the tracking actuator traces tracks. That is, if the MIRR signal is detected, it indicates that the main beam moves from one track to an adjacent track. The MIRR is shown in (c) of FIGS. 3A and 3B.
To jump tracks, the jump pulse forces the main beam to move between tracks, and after the track jump, the main beam may move between tracks due to the inertia of the tracking actuator even though the track movement should not occur. The tracking error signal TE, which is the differential signal between the MIRR and the side beam, is used to indicate whether the main beam moves from the inner track to the outer track or vice versa.
If the main beam moves from the inner track to the outer track, the F beam moves to the mirror and the amount of light increases. Since the E beam moves above the pit, the amount of light decreases and a positive error is generated in the TE indicated as an F-E signal. If the main beam moves from the outer track to the inner track, the E beam moves to the mirror and the amount of light increases. In addition, since the F beam moves above the pit, the amount of light decreases and a negative error is generated in the TE indicated as an F-E signal. The TE is shown in (e) of FIGS. 3A and 3B.
When the TE is sampled to make a digital signal, a track zero crossing (TZC) signal is generated. The TZC signal is shown in (f) and (g) of FIGS. 3A and 3B. As shown in FIGS. 3A and 3B, the TZC signal is sampled at rising and falling edges.
FIG. 1 is a block diagram showing an existing brake signal generating circuit that includes a latch 13, an inverter 15, a AND unit 17, first through third operation mode generators 21, 23 and 25, and switches SW1 and SW2.
In FIG. 1, the latch 13 receives the MIRR signal that detects the track movement of the main beam, latches the MIRR signal at the rising and falling edges of the TZC signal input to the clock terminal and outputs a latched mirror signal R_MIRR.
If the main beam moves from the inner track to the outer track, the R_MIRR signal is generated in inverse phase to the TZC signal due to the phase relation between the MIRR signal and the TZC signal. When the main beam moves from the outer track to the inner track, the signal R_MIRR is generated in the same phase as the TZC signal. The R_MIRR signal helps to identify whether the main beam moves from the inner track to the outer track or vice versa.
When the optical disc reproducing system normally reproduces data from a disc or jumps tracks, a low-level brake enable signal BRKENB is externally input. Then, when the track jump is complete, a low-level brake enable signal BRKENB is externally input so that the tracking pull-in can be performed using the brake signal TRBRK.
The AND unit 17 generates a brake signal TRBRK by performing an AND-operation on the R_MIRR signal and the BRKENB signal inverted by the inverter 15. That is, if the level of the BRKENB is low, the AND unit 17 generates a brake signal for controlling the switch SW2.
In response to the first control signal CTRL1, the first operation mode generator 21 generates a processing value of the gain and the phase of the TE, i.e., the first operation mode signal TRDREG, when the optical disc reproducing system is in a normal reproduction mode so that the tracking actuator traces the track normally. Here, CTRL1 is externally input and indicates an address and a command that control the operation of the first operation mode generator 21.
In response to the second control signal CTRL2, the second operation mode generator 23 generates a correction value of the tracking loop offset, i.e., the second operation mode signal TRDAVR. Here, the offset refers to approximately 200˜400 mV DC offset of the RFO signal caused by the light reflection when the main beam moves over the edge of the pit. Since the offset correction method is obvious to those with ordinary skill in the art, the method will not be explained here. In addition, CTRL2 is externally input and indicates an address and a command that control the operation of the second operation mode generator 23.
The third operation mode generator 25 generates a predetermined reference voltage as a fifth operation mode signal VREFS. The reference voltage is half of the power voltage, that is, ½ VDD.
The operation of the existing brake signal generating circuit 10 shown in FIG. 1 will now be described in more detail.
If a brake enable signal BRKENB at a high level is generated when the optical disc reproducing system is in a normal reproduction mode or a track jump mode, the brake signal TRBRK is generated in a low level and enables the switch SW2 to be connected to the first operation mode signal TRDREG. Then, the first operation mode generator 21 generates and externally outputs the first operation mode signal TRDREG. Therefore, in the normal reproduction mode, the tracking actuator is controlled to normally trace the tracks.
When the track jump is complete, if a brake enable signal BRKENB at a low level is generated, the brake signal TRBRK is generated in a high level and enables the switch SW2 to be connected to the output signal of the switch SW1. Then, in response to the brake selection signal BRKSEL, the switch SW2 is connected to the second mode operation signal TRDAVR or third operation mode signal VREFS. Here, the brake selection signal BRKSEL is input to control the switch SW1 and the logic level of the brake selection signal BRKSEL is determined by a microprocessor (not shown). The logic levels of the brake enable signal BRKENB and the brake signal TRBRK may be opposite to the ones described above depending on the circuit configuration.
In case the switch SW2 is connected to the third operation mode signal VREFS, the error, during a brake operation, in a track deviation direction is mute not to be output. Instead, a predetermined reference voltage is applied for brake operation and to prevent track skipping. That is, as shown in (j) of FIGS. 3A and 3B, if the main beam moves from the inner track to the outer track, the reference voltage is applied by muting the error processing of a positive movement direction. If the main beam moves from the outer track to the inner track, the reference voltage is applied by muting the error processing of a negative movement direction.
In case the switch SW2 is connected to the second operation mode signal TRDAVR, the predetermined reference voltage is not fed for the brake operation. Instead, a correction value of a tracking loop offset is output to prevent track skipping.
However, in the above method, the number of skipped tracks, which would be one or two or up to a few tens, is not considered to control the brake operation, Therefore, the brake control cannot be performed accurately.